Doppler catheter

ABSTRACT

A steerable catheter having a Doppler crystal at the tip to measure the velocity of blood in vivo--and inferentially the blood flow. The catheter includes two passageways, one passageway being exposed to the blood stream with the other passsageway containing the electrical leads to the Doppler crystal. The one passageway is dimensioned for receiving a wire guide for accurately manipulating the catheter. Preferably, the catheter incorporates an inflatable angio-balloon operable to distend the blood vessel in the region of a stenosis. Thus, blood flow can be determined in the region of the stenosis before and/or after the vessel is distended. The passageways are preferably defined by a pair of generally concentric tubes with the doppler crystal doughnut-shaped and sealingly disposed at the tip of the catheter.

This is a continuation of application Ser. No. 775,857, now U.S. Pat.No. 4,665,925.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention broadly relates to a catheter-like device and method formeasuring in vivo the velocity of a biological fluid, such as blood. Inparticular, it relates to a velocity measuring, Doppler crystal,steerable catheter which incorporates an angioplasty, expandable balloonfor identifying and treating arterial stenoses.

2. Description of the Prior Art

Coronary artery disease is quite common and is usually manifested in aconstriction or stenosis in the arterial tree. An inability toadequately increase flow through stenosed coronary arteries issymptomatic of coronary artery disease. Coronary vasodilator reserve ormaximum coronary blood flow is a key indicator of the adequacy of thearterial tree. That is, the coronary vasodilator reserve correlates tothe ability of the arterial tree to respond to an increase in myocardialoxygen demand. Hyperemic response or increased blood flow caused byvessel dilation has long been used as a measure of coronary vasodilatorreserve. Progressive coronary artery disease can lead to increasedvessel stenosis, selective lesions and gradual diminution of thereactive hyperemic response.

Since the ability to adequately analyse changes in blood flow throughstenosed coronary arteries is important in properly evaluating theextent of coronary artery disease, many diagnostic tests have beendevised to identify the flow limiting characteristics of a particularstenosis. The most common procedure used to predict the physiologicimportance of a coronary stenosis is the use of the coronaryarteriogram. Such a coronary arteriogram (or angiogram) involves theinjection of a radiopaque material (angiodye) into the arterial tree andsubsequent radiographic analysis of the extent of the stenosis. Suchangiographic analysis is often undertaken concurrent with the inducementof a hyperemic response. Typically, the angiodye induces a certaindegree of hyperemic response with other pharmacological agents (e.g.dipyridamole, meglumine diatrizoate, etc.) often used to increase thedegree of hyperemia.

Such arteriographic prediction of the effect of coronary arterialdisease has recently been criticized for its erratic reliability. Forexample, interobserver variability error has been shown to be sometimessignificant in arteriograph analysis. Further, arteriograph analysisinvolves a longitudinal cross-sectional view of the vessel in questionand usually compares the region in question with the immediatelyadjacent vessel region. This protocol assumes that the region of thevessel adjacent the lesioned section is normal. Of course, thisassumption is often incorrect in that the adjacent region of the vesselmay have moderate to severe stenosis which would be readily apparent ona histological or cross-sectional view of the vessel.

In fact, in a recent study (White, et al., Interpretation of theArteriogram, 310 New Eng. J. Med. 819-824, (1984)) the authors found nosignificant correlation between the angiographically determinedpercentage of coronary obstruction and the hyperemic response. Thus, itwas concluded that the coronary arteriogram often provides inaccurateinformation regarding the physiological consequences of the coronaryartery disease.

Still other researchers have concluded that the arteriogram is onlyreliable in identifying a stenosis with greater than about 80%constriction of the vessel. However, marked impairment of the coronaryvasodilator reserve can also occur in the 30-80% constriction range, butsuch stenoses are often not identified by the arteriogram. Thus, whilethe coronary arteriogram is useful in giving anatomic definition tocoronary occlusions, it often provides little information concerning thehemodynamic consequences until near total occlusion of the vesseloccurs.

In light of the shortcomings of arteriographic prediction, other methodshave been proposed to more accurately analyze coronary stenosis. Forexample, computer-based quantitative coronary angiographic, coronaryvideo-densitometery and radionuclide-perfusion techniques have all beenemployed. However, all of the techniques present other difficulties asprediction tools. For example, radionuclide techniques measure regionalblood flow, but do not permit continuous assessment of coronary bloodflow and are only accurate at low blood flow rates.

In response to the serious drawbacks with current analytical methodsemployed in assessing the physiological effects of coronary arterialdisease, several researchers have experimented with utilizing a catheterwhich incorporates a Doppler mechanism to measure in vivo the bloodvelocity (and inferentially blood flow rate). For example, G. Cole andC. Hartley in Pulsed Doppler Coronary Artery Catheter, 56 Circulation18-25 (1977) proposed a pulse Doppler crystal fitted at the end of acatheter for in vivo analysis. Similarly, Wilson, et al., DiagnosticMethods, 72 Circulation 82-92 (1985) proposed a catheter having aradially-oriented Doppler crystal.

Doppler techniques for measuring flow are advantageous because rapid anddynamic changes in flow can be detected, real-time recording can beobtained and such techniques are adapatable for miniaturization. Infact, past studies with Doppler catheters appear to have validated theaccuracy of such Doppler measurements as an indication of flow. Thesestudies contend that the obstruction of blood flow caused by thecatheter is insignificant and that the velocity measurements obtainedare linearly related to the actual flow rates. Further, these velocitymeasurements purportedly accurately track actual flow rates throughouthyperemic response.

To date, however, such Doppler catheters are largely impractical forclinical applications and are beset with technical difficulties. Forexample, such past Doppler catheters have been of such a size thatstenoses located in most parts of the arterial tree cannot beeffectively avaluated. Further, such past Doppler-based catheters havenot been effectively steerable and thus cannot be accurately placedwithin the arterial tree. In fact, signal instability and error has beenoften encountered due to catheter placement and orientation relative tothe vessel walls and flow axis. Of course, of primary consideration in aDoppler-based catheter design is the safety to the patient by theelectrical isolation of the Doppler crystal.

SUMMARY OF THE INVENTION

The problems outlined above are largely solved by the steerable,catheter-like, velocity-measuring device and method of the presentinvention. The device hereof is achieved on a very smallscale--approximately number three French (0.039 inch diameter)--forplacement in many locations previously unattainable in the arterialtree. The device is designed to accept a conventional wire guide, whichenables the steerable placement of the device at a desired location. Inone embodiment, the device incorporates an inflatable angio-balloonwhich enables treatment of stenosis and analysis of the blood velocitythrough this stenosis without withdrawal of the catheter-like device.

Broadly speaking, the catheter-like device includes an elongated,flexible body having first and second passageways longitudinallyoriented within the body with a Doppler mechanism attached adjacent thedistal end of the body for determining the velocity of a biologicalfluid. The Doppler mechanism includes electrical leads operably disposedwithin one of the passageways, while the other passageway is adapted forexposure to the biological fluid. Preferably, the body is tubular withan inner channel structure operably received within the body to defineand separate the two passageways. The Doppler mechanism preferablyincorporates a Doppler crystal attached adjacent the distal end of thebody.

In a preferred form, the inner channel is tubular and coaxially alignedwithin the body to define a central lumen within the channel and anannular lumen between the channel and body. In this embodiment theDoppler crystal is a generally flat, annular, doughnut-shapedpiezoelectric ceramic having a central aperture through which thechannel extends. The Doppler crystal is sealingly attached adjacent thedistal end of the body. The electrical leads are received in the annularlumen in isolation from the biological fluid. The central lumen is notonly adapted for receiving a steerable wire guide, but can equally beused to inject pharmacological agents or angiodye into the arterialtree.

In a preferred embodiment, an expansion means is operably coupled to thebody and is operable for selectably exerting outward pressure againstthe vessel. Preferably, a pneumatic passageway extends longitudinallythrough the body. The expansion means preferably includes a flexible,balloon-like sleeve coupled to the pneumatic passageway which isselectably outwardly expandable to occlude or distend a portion of theblood vessel.

The device of the present invention lends itself to a method ofidentifying and treating stenoses in the arterial tree, particularlywhen utilizing the embodiment of the device which incorporates anangio-balloon proximate to the distal end of the device. With a wireguide received in the device, the catheter-like device is easilyinserted and steerable in the arterial tree. The wire guide ismanipulated to position the catheter in the region of a stenosis. Withthe device in place, the Doppler crystal is utilized to measure thevelocity of the blood in the region of the stenosis. The Doppler crystalcan be operated to determine the velocity of the blood both before andafter the angio-balloon is expanded in the region of the stenosis. Oneoption is to expand the angio-balloon to distend the arterial vessel inthe region of the stenosis, in a manner similar to conventionalangioplasty techniques. Another option is to expand the angio-balloononly to the extent of occluding the vessel for a short period of time toinduce a hyperemic response. Of course, the Doppler mechanismcontinuously provides velocity measurements throughout a hyperemicresponse.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary view with some parts broken away for clarity, ofthe preferred embodiment of the device of the present invention;

FIG. 2 is an enlarged, fragmentary, longitudinal view in partial sectionof the distal end of a device in accordance with the present invention;

FIG. 3 is a sectional view taken along line 3--3 of FIG. 2; and

FIG. 4 is a sectional view taken along line 4--4 of the deviceillustrated in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to the drawing, a velocity measuring, catheter-like device10 in accordance with the present invention is illustrated. Broadlyspeaking the device 10 includes an elongated, flexible, tubular body 12,Doppler mechanism 14, and expansion means 16. The device 10 isdimensioned and adapted for insertion in vivo into the arterial tree ofa patient.

In more detail, the body 12 includes a distal section 20 extendingbetween the Doppler mechanism 14 and a branch connector 22. Dividingfrom the branch connector 22 towards the proximal end is a pneumaticsection 24 and a section 26 (lower left portion of FIG. 1). Thepneumatic section 24 terminates in a Luer fitting 28 which is adaptedfor connection to a selectable pneumatic source. Section 26 terminatesin a Doppler electrical connector 30 joined to the section 26 and amulti-purpose Luer fitting 32.

A flexible, elongated, inner, tubular channel 40 extends from the Luerfitting 32 (FIG. 1) through the distal section 20 (see FIG. 2). Thetubular, infusion channel 40 defines a central, infusion lumen 42 (seeFIGS. 3, 4). Turning to FIG. 2, the distal section 20 includes an outerflexible tube 44 which, towards the distal end, converges inwardly intoclosely spaced relation to the inner channel 40. The annular regionbetween the inner walls of the tube 44 and outer walls of the channel 40defines annular lumen 46 (see FIGS. 2-3).

The expansion means 16 includes an expandable flexible balloon-likesleeve 50 sealingly fitted circumferentially to the outer tube 44 asshown in FIG. 2. As illustrated in FIGS. 2-3, and a chord structure 52longitudinally extends through the distal section 20 between the sleeve50 and branch connector 22. The chord structure 52 and a portion of theinner wall of the tube 44 (see FIG. 3) defines a pneumatic passageway 54which is operably connected between the sleeve 50 and pneumatic section24. An aperture 56 through the tube 44 (FIG. 2) connects the passageway54 with the interior of the sleeve 50. A pair of radiopaque ring markers58 are operably disposed about the tube 44 inside of the sleeve 50.

In more detail, the Doppler mechanism 14 incorporates a pair ofelectrical leads 60 operably connected to the electrical connector 30and passing through the section 26 (see FIG. 1) and into the distalsection 20 (see FIG. 2). As shown in FIG. 2, the electrical leads 60 aredisposed in the annular lumen 46 defined by the region between thechannel 40 and tube 44 (see FIGS. 2-3). The Doppler leads 60 terminateat the washer-like, flat, doughnut-shaped Doppler crystal 62 which issealingly disposed about the channel 40. The Doppler crystal 62 in thepreferred embodiment is a piezoelectric ceramic crystal comprising alead-zirconate-titanate material which is about 0.003 inch in thicknessand 0.035 inch in outside diameter. The Doppler crystal 62 is designedto resonate at 20 megaHertz with a voltage applied to generate a 20megaHertz signal (acoustic tone). The crystal 62 is a single crystal tooperate as a pulsed Doppler transducer, acting alternately as atransmitter and receiver.

An encapsulant 64 is sealingly disposed about the Doppler crystal 62. Asshown in FIG. 2, the tip of the channel 40 extends slightly past themarginal periphery of the tube 44 and past the crystal 62, which incombination with the encapsulant 64 provides effective isolation of theDoppler crystal 62 and leads 60 from the biological fluid when in use inthe arterial tree.

The principal of pulsed Doppler operation in measuring velocity of afluid is known in the art, for example as explained by C. Hartley and J.Cole in Pulsed Doppler Flow Measurement, 37 J. of App. Phys. 626-629(1974) (incorporated by reference herein). In the embodiment illustratedin the drawing, the Doppler crystal 62 is a single piezoelectric ceramiccrystal having a master oscillator frequency of 20 megaHertz and ispulsed at a repetition frequency (prf) of 62.5 kiloHertz. Each pulse isapproximately one-half microsecond in duration.

Those skilled in the art will appreciate that with the device 10 inplace in the arterial tree, each acoustic tone burst is transmittedthrough the blood and reflected by various structures, for example redblood cells, vessel wall, plaque, etc. Depending on the distance of eachreflecting structure, the returning acoustic signals received by theDoppler crystal 62 are separated in time. An adjustable receiver gate isincorporated to select signals reflected from the structures at aspecified distance from the crystal 62. The reflected signals receivedby the Doppler crystal 62 are amplified and compared in phase andfrequency to the master oscillator signal of 20 megaHertz.

The difference in frequency between the amplified reflected signal andthe master oscillator signal is the Doppler shift. The Doppler shift(Δf) is defined by the Dopper equation:

    Δf=2FV/c cos θ

where F is the transmitted frequency; V is the velocity of the fluid; cis velocity of sound in the fluid; and θ is the angle between the fluidflow axis and the acoustic axis. Since transmitted frequency (F),velocity of sound in the fluid (c), and the angle (θ) are constant, theDoppler shift (Δf) is linearly related to the velocity of the fluid (V).This assumes that the device 10 is in a stable position in the arterialtree and that the angle (θ) remains constant. As used in the presentapplication the term "velocity" or "velocity of the fluid" means eitherthe absolute velocity or a number linearly related to the absolutevelocity.

ALTERNATIVE EMBODIMENTS

Those skilled in the art will appreciate that many structuralalternatives exist to the preferred embodiment illustrated in thedrawing. For example, in a broad sense, the device 10 need notincorporate the expansion means 16 to be useful in the diagnosis ofcoronary artery disease. In fact, prototypes have been constructed usinga USCI (United States Catheters and Instruments) Rentrop reperfusioncatheter with the Doppler mechanism 14 attached to the tip. Theseprototypes incorporated a 4 French outermost tubular main body (1.3millimeters) which tapered to a tip 3 French in size (1 millimeter). Thecatheter was 110 millimeters long having an internal diameter of 0.020inches running the length thereof. An internal channel tubing was fittedwithin this body and had a 0.018 inch outside diameter to define anannular lumen between the channel and body. The inner diameter of theinner channel was 0.0155 inches and defined an infusion or centrallumen. A 0.014 inch wire guide was receivable in the central lumen. Theelectrical leads ran in the annular lumen with a Doppler crystal mountedat the tip of the catheter. The Doppler crystal in the prototypecomprised a thin disc about 0.003 inches thickness with an outsidediameter of 0.035 inches. An aperture of about 0.022 inches wascentrally located to give the Doppler crystal a doughnut-shapedconfiguration. The Doppler crystal was interfitted over the channel andinsulated and attached by epoxy between the channel and body. Thechannel terminated just beyond the Doppler crystal at the distal tip ofthe catheter.

Still other alternative exists. In the preferred device illustrated inthe drawing, the Doppler crystal 62 is attached at the distal tip of thedevice 10 and axially oriented. This installation and orientation hasbeen found preferable in giving good signal stability and accuracy. Asan alternative, the Doppler crystal 62 can be installed in a more radialor oblique orientation. However, it is speculated that a radialorientation might provide inherent inaccuracies due to placement of thedevices in the arterial vessel with the crystal adjoining the vesselwall. Measurement of the fluid velocity would, of course, be impossibleunder these circumstances. Additionally, it is deemed preferable to havethe acoustic axis generally linearly aligned with the fluid flow axis ascompared with the oblique angle produced if the Doppler crystal 62 isradially oriented relative to the body 12. Doppler shift is usually moreaccurately determined with the axes aligned.

Still other alternatives exist in the precise configuration of thedevice 10. For example, the device 10 of the preferred embodimentenvisions a catheter-like device similar to a conventional angioplasticcatheter which incorporates the Doppler mechanism. However, it isanticipated that the device 10 of the present invention may beincorporated into a mechanism resembling a steerable wire guide havingthe Doppler mechanism at the tip, which might be inserted through acatheter when it is desired to take the velocity measurements.

As another alternative, it will be readily appreciated that the innerand outer dimensions of the channel 40 and tube 44 are not critical.That is, the outer surface of the channel 40 and inner surface of thetube 44 may in fact be adjoining with the electrical leads 60 compressedtherebetween. Alternatively, the electrical leads 60 may be incorporatedintegral with either the channel 40 or tube 44.

As still another alternative, those skilled in the art will appreciatethat the electrical leads 60 can be routed through other passages out ofpossible contact with the biological fluid. For example, (see FIG. 3)the electrical leads 60 could be routed through the pneumatic passageway54 with or without the channel 40 or sleeve 50 incorporated in thedevice.

OPERATION

In use, the device 10 is inserted into the arterial tree through aJudkins-type guiding catheter. The device 10 is preferably preloadedwith a teflon-coated steerable guidewire (e.g. 0.014 inch O.D.USCI-type) through the central lumen 42. After passing theguidewire/device 10 combination through the guiding catheter to thecoronary ostium, the guidewire is used to selectively place the distalend of the device 10 proximate to the coronary stenosis under study.

It is assumed that this operation takes place in a conventional cardiaccatheterization laboratory. It is important throughout the velocitymeasurements to insure that the distal tip of the device 10 remains in agenerally stable position. When initially positioning the distal tip,small injection of an angiodye may be injected through the Luer fitting32 into the central lumen 42 into the bloodstream to verify the positionof the distal tip. Doppler measurements are then taken with the rangegate adjusted and the position of the distal tip varied to obtain themaximum velocity signal.

After the position of the distal tip of the device 10 is verified andstabilized, the guidewire can be withdrawn from the device 10. In anyevent, after the initial velocity measurements are made, a hyperemicresponse will typically be induced to effectively analyze the coronaryvasodilator reserve capacity. Several methods are available for inducingthe hyperemic response. In the preferred method, the sleeve 50 isexpanded in the area of the stenosis until occlusion of the vessel isobtained. Advantageously, the Doppler mechanism 14 operates to verifythe occlusion. The occlusion is held for approximately 20 seconds thenreleased; this technique has been found to induce a hyperemic response.Other techniques are of course available. For example, a pharmacologicalagent such as dipyridamole or meglumine diatrizoate may be injected toinduce the hyperemic response. As a third alternative, contrast media orangiodye injection will in most cases induce a sufficient hyperemicresponse for proper analysis.

At some stage, coronary angioplasty can be performed by expanding thesleeve 50 to dilate or distend the vessel. Of course, conventionalangiographic assessment of the efficacy of the dilation can be utilizedor alternatively, the dilation can be performed at progressivelyincreased pressures and the effectiveness analyzed by the velocitymeasurements. For example, before and after the first dilation by theexpansion means 16, the Doppler mechanism 14 can be operated todetermine the blood flow velocity before and after the dilation andhence the efficacy of the dilation. Subsequent dilation can be made asneeded.

It will be appreciated that the device 10 of the present invention is asignificant advance over previous in vivo coronary catheters and allowsfor a significant advance in the diagnosis and treatment of coronaryarterial disease. The criticisms of the use of conventional coronaryarteriograms as a method of measuring the extent of coronary stenosisis, to some extent, valid. As previously discussed, some studies suggestthat conventional arteriograms are particularly inaccurate where thestenosis is less than approximately an 80% occlusion. In all cases, itshould be readily apparent that an apparatus which more directly takesflow measurements is ideal in analyzing coronary vasodilator reservecapacity. The device 10 of the present invention provides real timeanalysis by providing continuous velocity measurements which arelinearly related to blood flow. This is in sharp contrast toconventional angiograms which only accurately identify regions ofpossible stenoses, but not the physiological importance of suchstenoses.

In practice, it has been found that the velocity measurements are veryaccurate in evaluating the flow. That is, various studies have shownthat maximal coronary reactive hyperemic response is relatively constantwhether or not a catheter the size of the device 10 is present or absentin the artery being investigated. This implies that the obstruction ofblood flow by the device 10 is minimal during the hyperemic response.Further, vessel diameter expansion during hyperemic response has beenfound to minimally affect the accuracy of the velocity measurements asan indication of flow. Additionally, the range gating of the pulsedDoppler crystal of the device 10 of the present invention allows forselective analysis of a target region a sufficient distance(approximately 2-10 mm) away from the catheter tip to avoid tip inducedturbulent flow which would affect the accuracy of the velocitymeasurements.

Utilizing the device 10 of the present invention, coronary arterydisease is more effectively identified and treated than by use ofconventional methods and devices. When used in conjunction withconventional angiograms and angioplasty procedures, the device andmethod of the present invention present a significant advance in theart.

I claim:
 1. A steerable catheter which is operable to measure the fluidvelocity in a fluid-carrying vessel, the catheter comprising:anelongated, flexible, tubular body having a distal end and being operablymanipulable in the vessel; a channel structure operably received andgenerally longitudinally aligned within said body, said channelstructure defining a lumen which, with the catheter inserted into thevessel, is isolated from the fluid within the vessel; a structuredefining a passageway which, with the catheter inserted into the vessel,is adapted for operable communication with the fluid within the vesseland for receiving a wire steering guide to selectively position saiddistal end in the vessel; and Doppler means for measuring the velocityof the blood through the vessel includinga Doppler crystal disposedadjacent said distal end, the Doppler crystal having a flat faceoriented generally perpendicular to the longitudinal axis of said body,said flat face defining an acoustic axis generally aligned with thelongitudinal axis of said body so that the acoustic axis is manipulableinto linear alignment with the fluid flow axis in the vessel, andelectrical leads connected to the crystal and disposed in said lumen inisolation from the fluid with the catheter inserted in the vessel. 2.The catheter according to claim 1, wherein said channel structure andbody are tubular, with the channel structure concentrically locatedwithin said body.
 3. The catheter according to claim 2, said passagewaybeing cylindrical and defined by said tubular channel and said lumenbeing defined by the annular space between the body and channel.
 4. Thecatheter according to claim 3, said Doppler crystal beingdoughnut-shaped to overlay said annular lumen with the passagewayexposed.
 5. The catheter according to claim 1, said Doppler crystalcomprising a lead-zirconate-titanate piezoelectric ceramic.
 6. Thecatheter according to claim 1, said passageway being defined by aportion of the inner wall of said body and a planar surface disposedalong a chord of the circular cross-section of said body.
 7. Thecatheter according to claim 1, said lead means received in said lumenbeing non-integral with the channel structure.
 8. The catheter inaccordance with claim 1, the channel structure extending beyond theDoppler crystal to isolate the passageway from the Doppler crystal. 9.The catheter in accordance with claim 1, the body being dimensioned forpositioning in a fluid-carrying vessel and having an outer diameter lessthan about 0.040 inches.
 10. The catheter in accordance with claim 1,said passageway defining structure extending substantially along theentire length of the body.
 11. The catheter according to claim 1, saidpassageway-defining, tubular channel structure extending distal to saidDoppler crystal.